1. Field of the Invention
The present invention relates to magneto-optical disk apparatuses employing a magnetic field and a laser beam to reproduce a signal from a magneto-optical recording medium having a magnetic domain formed therein to record a signal, and methods of reproducing the same.
2. Description of the Background Art
A magneto-optical recording medium has been noted as a recording medium which is rewritable, has a large storage capacity and is highly reliable, and it has been put to practical use as computer memory or the like. Furthermore, in recent years a magneto-optical recording medium having a storage capacity of 6.0 Gbytes is standardized as the Advanced Storaged Magneto Optical (AS-MO) disk standard and it is about to be put to practical use.
Furthermore, there has also been proposed a magneto-optical recording medium having a recording capacity of 14 Gbytes allowing a magnetic domain to be transferred from a recording layer to a reproducing layer and enlarged in the reproducing layer to reproduce a signal. In this magnetic domain enlargement and reproduction system, a signal is reproduced by applying to a magneto-optical recording medium an alternating magnetic field having a predetermined angle to an in-plane direction of the recording medium. More specifically, as shown in FIG. 26A, the magneto-optical recording medium includes a recording layer 5 having a magnetic domain of a different length and in the magnetic domain enlargement and reproduction system an alternating magnetic field is applied and a laser beam is directed to transfer each magnetic domain from recording layer 5 via a non-magnetic layer 4 to a reproducing layer 3 and enlarge it therein. The enlarged magnetic domain is detected by a laser beam. Herein, the alternating magnetic field is applied to recording layer 5 at substantially the center of each magnetic domain. If a magnetic domain in recording layer 5 varies in length a magnetic field leaking from the magnetic domain of recording layer 5 via non-magnetic layer 4 to reproducing layer 3 also has a different intensity profile. A leaking magnetic field for a magnetic domain having a unit domain length has an intensity increasing in the direction from an end of the magnetic domain to the center thereof. A leaking magnetic field for a magnetic domain having a length more than twice the unit domain length, has a high intensity at an end of the magnetic field and a low intensity at the center thereof. As such, if an alternating magnetic field is applied to each magnetic domain at the center thereof, magnetic domains having different lengths cannot be accurately transferred to and enlarged in reproducing layer 3.
To overcome this disadvantage, there has been proposed applying to a magnetic domain at an end thereof (i.e., a boundary between magnetic domains) an alternating magnetic field Hex1 having a predetermined angle to an in-plane direction of a magneto-optical recording medium, to enlarge and reproduce the magnetic domain. Recording layer 5 has magnetic domains each having a boundary with a leaking magnetic field 190-194 and when the boundaries with leaking magnetic fields 190, 192, 194 receive alternating magnetic field Hex1 magnetic domains 195-197 have their respective ends readily, initially transferred to reproducing layer 3. This principle will now be described with reference to FIGS. 27A-27D. As shown in FIG. 27A, if a signal is reproduced, reproducing layer 3 is initialized, magnetized in a predetermined direction. Furthermore, recording layer 5 has magnetic domains 220-222 having a signal recorded therein. Herein, a leaking magnetic field of magnetic domain 221 in a vertical direction, i.e., a direction to reproducing layer 3 has an intensity profile as shown in FIG. 27B.
In contrast, a leaking magnetic field of magnetic domain 221 in an in-plane direction has an intensity profile as shown in FIG. 27C. More specifically, it is a leaking magnetic fields having opposite directions and a uniform intensity at opposite ends of magnetic domain 221 and if the leaking magnetic field at the boundary of magnetic domains 220 and 221 is directed in the direction from magnetic domains 221 to 220 then the leaking magnetic field at the boundary of magnetic domains 221 and 222 is directed in the direction from magnetic domains 221 to 222. As such, a leaking magnetic field in the in-plane direction that comes from magnetic domain 221 to affect reproducing layer 3 has opposite directions and a uniform intensity, and a magnetic force acting to invert the reproducing layer 3 magnetization in the direction of the magnetic domain 221 magnetization is balanced at the opposite ends of magnetic domain 221. As a result, magnetic domain 221 does not have one end thereof preferentially transferred to reproducing layer 3.
However, when magnetic domain 221 receives a magnetic field containing magnetic field component having the in-plane direction, a leaking magnetic field in the in-plane direction that comes from magnetic domain 221 has an intensity profile as shown in FIG. 27D, and when a magnetic field is applied in a direction from magnetic domains 221 to 220 a leaking magnetic field 225 at the boundary of magnetic domains 221 and 220 is intensified as compared to a leaking magnetic field 226 at the other boundary thereof. As such, a leaking magnetic field 224 acts on the reproducing layer""s magnetic domain 223 corresponding to an end of magnetic domain 221 closer to magnetic domain 220 to readily invert the magnetic domain 223 magnetization in the same direction as the magnetic domain 221 magnetization. As a result, if magnetic domain 221 is transferred to reproducing layer 3 it is transferred initially at an end thereof closer to magnetic domain 220 and in reproducing layer 3 at magnetic domain 223 there is created a species domain magnetized in the same direction as magnetic domain 221 is magnetized, and a magnetic field having a direction perpendicular to reproducing layer 3 that is the same direction as magnetic domain 221 is magnetized is applied to enlarge the species domain.
Thus, applying a magnetic field containing a magnetic field component having an in-plane direction facilitates transferring a magnetic domain to a reproducing layer.
Again with reference to FIGS. 26A and 26B, when alternating magnetic field Hex1 is applied to a magneto-optical recording medium at a predetermined angle to an in-plane direction of the recording medium and it is thus applied to each magnetic domain at a boundary thereof, and a laser beam LB is directed to enlarge and reproduce the magnetic domain, the following problem arise.
More specifically, when alternating magnetic field Hex1 is applied at a timing as shown in FIG. 26B at (a) and in the direction as indicated in FIG. 26A, only at a timing at which a positive (+) magnetic field 198 is applied to the boundaries of the magnetic domains having leaking magnetic fields 190, 192 and 194 recording layer 5 has magnetic domains 195-197 each transferred to and enlarged in reproducing layer 3 and a reproduced signal (b) is detected as shown in FIG. 26B. As such, if alternating magnetic field Hex1 is applied to the domains"" boundaries having leaking magnetic fields 191 and 193, the magnetic domains are not transferred from recording layer 5 to reproducing layer 3. As a result, the magnetic domain 195 length having a domain length larger than a unit domain length cannot be detected accurately nor can magnetic domain 201, a domain adjacent to domain 195, be detected. More specifically, in reproduced signal (b) a component 199 indicates a start point of magnetic domain 195 and the component detected subsequent to component 199 is a component 200. As such the end point of magnetic domain 195 is thus not clearly indicated nor is the start point of magnetic domain 201, a domain adjacent to domain 195.
As such, if a magnetic domain is enlarged and reproduced by applying only alternating magnetic field Hex1 having a predetermined angle to an in-plane direction having a direction of a track of a magneto-optical recording medium, the magnetic domain is transferred and enlarged only at a boundary thereof having a leaking magnetic field intensified and it is not transferred or enlarged at a boundary thereof failing to have a leaking magnetic field intensified. As such, accurate signal reproduction cannot be achieved.
The present invention therefore contemplates a magneto-optical disk apparatus capable of accurately enlarging and reproducing a magnetic domain, and a method of reproducing the same.
The present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a magnetic head applying a first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium, and applying a second alternating magnetic field to the magnetic domain at the other edge existing in a direction of a track of the magneto-optical recording medium; and an optical head directing a first laser beam to the one edge and a second laser beam to the other edge, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
The present magneto-optical disk apparatus allows a magneto-optical recording medium to have any magnetic domain formed therein with one edge thereof receiving a first alternating magnetic field containing a magnetic field component increasing a component of a leaking magnetic field created at one edge and having an in-plane direction of the recording medium, and with the other edge receiving a second alternating magnetic field containing a magnetic field component increasing a component of a leaking magnetic field created at the other edge and having an in-plane direction of the recording medium. As such, each magnetic domain has opposite ends initially transferred and enlarged in reproducing a signal.
As such in the present invention if a magneto-optical recording medium has a magnetic domain having a different domain length to record a signal therein a reproduced signal attributed to a domain length can be detected and it can thus be reproduced accurately.
Furthermore, the present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a drive signal generation circuit generating a drive signal including a first timing at which a first alternating magnetic field is applied and a second timing at which a second alternating magnetic field is applied; a magnetic head operating based on the drive signal to apply the first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium, and operating based on the drive signal to apply the second alternating magnetic field to the magnetic domain at the other edge existing in the direction of the track; and an optical head directing a first laser beam to the one edge and a second laser beam to the other edge, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present magneto-optical disk apparatus there is generated a drive signal for generating for one edge of any magnetic domain in a magneto-optical recording medium a first alternating magnetic field containing a magnetic field component increasing a component of a leaking magnetic field created at one edge and having an in-plane direction of the recording medium, and for the other edge of the magnetic domain in the magneto-optical recording medium a second alternating magnetic field containing a magnetic field component increasing a component of a leaking magnetic field created at the other edge and having an in-plane direction of the recording medium. In response to the generated drive signal the first and second alternating magnetic fields are applied to the magneto-optical recording medium. Furthermore, one edge receives a first laser beam and the other edge receives a second laser beam. Consequently, the magneto-optical recording medium has each magnetic domain having opposite ends initially transferred and enlarged in reproducing a signal.
As such in the present invention if a magneto-optical recording medium has a magnetic domain having a different domain length to record a signal therein a reproduced signal attributed to a domain length can be detected and it can thus be reproduced accurately.
Furthermore, the present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a first magnetic head applying a first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium; a second magnetic head applying a second alternating magnetic field to the magnetic domain at the other edge existing in the direction of the track; a first optical head directing a first laser beam to the first edge; and a second optical head directing a second laser beam to the other edge, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present magneto-optical disk apparatus, a first magnetic head applies a first alternating magnetic field to any magnetic domain at one edge and a second magnetic head applies a second alternating magnetic field to any magnetic domain at the other edge. Furthermore, a first optical head directs a first laser beam to any magnetic domain at one edge and a second optical head applies a second laser beam to any magnetic domain at the other edge. As such, a magneto-optical recording medium has any magnetic domain having opposite ends initially transferred and enlarged in reproducing a signal.
Thus in the present invention if the first magnetic head applies the first alternating magnetic field having a center matching an optical axis of the first laser beam directed from the first optical head and the second magnetic head applies the second alternating magnetic field having a center matching an optical axis of the second laser beam directed by the second optical head, the first magnetic head is not required to be close to the second magnetic head (or the optical axis of the first laser beam is not required to be that of the second laser beam) to allow the magneto-optical recording medium to have any magnetic domain having opposite ends initially transferred and enlarged to accurately reproduce a signal.
Furthermore the present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a drive signal generation circuit generating a first drive signal including a first timing at which a first alternating magnetic field is applied, and a second drive signal including a second timing at which a second alternating magnetic field is applied; a first magnetic head operating based on the first drive signal to apply the first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium; a second magnetic head operating based on the second drive signal to apply the second alternating magnetic field to the magnetic domain at the other edge existing in the direction of the track; a first optical head directing a first laser beam to the one edge; and a second optical head directing a second laser beam to the other edge, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present magneto-optical disk apparatus a drive signal generation circuit generates a first drive signal provided to apply a first alternating magnetic field to a magnetic domain at one edge and a second drive signal provided to apply a second alternating magnetic field to a magnetic domain at the other edge. In response to the first drive signal a first magnetic head applies the first alternating magnetic field to a magneto-optical recording medium. In response to the second drive signal a second magnetic head applies the second alternating magnetic field to the magneto-optical recording medium. A first optical head directs a first laser beam to one edge of a magnetic domain created in the magneto-optical optical recording medium. A second optical head directs a second laser beam to the other edge of a magnetic domain created in the magneto-optical recording medium. Thus the magnetic domain has opposite ends initially enlarged in reproducing a signal.
Thus in the present invention two drive signals can be used to apply an alternating magnetic field allowing any magnetic domain to have opposite ends initially transferred and enlarged. Thus a signal can be reproduced accurately.
Furthermore, the present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a magnetic head applying a first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium, and applying a second alternating magnetic field to the magnetic domain at the other edge existing in a direction of a track of the magneto-optical recording medium; and an optical head directing a first laser beam to the one edge and a second laser beam to the other edge; and a composite circuit compositing together a first magneto-optical signal reproduced by applying the first alternating magnetic field and directing the first laser beam and a second magneto-optical signal reproduced by applying the second alternating magnetic field and directing the second laser beam, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present magneto-optical disk apparatus a first magneto-optical signal is detected at one edge of any magnetic domain created in a magneto-optical recording medium and a second magneto-optical signal is detected at the other edge of any magnetic domain created in the magneto-optical recording medium. The first and second magneto-optical signals detected are composited together.
Thus in the present invention a reproduced signal can be detected from opposite ends any magnetic domain and a signal can be reproduced accurately without depending on a domain length of each magnetic domain.
Furthermore, the present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a drive signal generation circuit generating a drive signal including a first timing at which a first alternating magnetic field is applied and a second timing at which a second alternating magnetic field is applied; a magnetic head operating based on the drive signal to apply the first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium, and operating based on the drive signal to apply the second alternating magnetic field to the magnetic domain at the other edge existing in the direction of the track; and an optical head directing a first laser beam to the one edge and a second laser beam to the other edge; and a composite circuit compositing together a first magneto-optical signal detected at the first timing and a second magneto-optical signal detected and the second timing, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present magneto-optical disk apparatus, a first alternating magnetic field is applied to any magnetic domain at one edge at a first timing included in a drive signal generated by a drive signal generation circuit and a second alternating magnetic field is applied to any magnetic domain at the other edge at a timing included in the drive signal generated by the drive signal generation circuit. Furthermore, a first laser beam is directed to any magnetic domain at one edge and a second laser beam is directed to any magnetic domain at the other edge. The two magneto-optical signals detected are composited together.
Thus in the present invention a drive signal can be used to apply alternating magnetic fields to any magnetic domain at opposite ends thereof to detect two magneto-optical signals from a magnetic domain at opposite ends. Since the detected two magneto-optical signals are composited together, a reproduced signal can be obtained depending on a domain length of each magnetic domain and a signal can thus be reproduced accurately.
Furthermore the present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a first magnetic head applying a first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium; a second magnetic head applying a second alternating magnetic field to the magnetic domain at the other edge existing in the direction of the track; a first optical head directing a first laser beam to the one edge; and a second optical head directing a second laser beam to the other edge; and a composite circuit compositing together a first magneto-optical signal reproduced by applying the first alternating magnetic field and directing the first laser beam and a second magneto-optical signal reproduced by applying the second alternating magnetic field and directing the second laser beam, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present magneto-optical disk apparatus, two magnetic heads are used to apply two alternating magnetic fields to any magnetic domain at opposite ends and two optical heads are used to direct two laser beams to any magnetic domain at opposite ends. Then, attributed to any magnetic domain having opposite ends initially transferred and enlarged, two magneto-optical signals are detected, and the detected two magneto-optical signals are composited together.
As such in the present invention if the first alternating magnetic field has a center matching an optical axis of the first laser beam and the second alternating magnetic field has a center matching an optical axis of the second laser beam then attributed to any magnetic domain having opposite ends initially transferred and enlarged there can be detected two magneto-optical signals which are in turn composited together to obtain a reproduced signal depending on a domain length of each magnetic domain. Furthermore, the first alternating magnetic field is not required to have its center close to the center of the second alternating magnetic field (or the first laser beam is not required to have its optical axis close to the optical axis of the second laser beam) and two magnetic heads or two optical heads can thus be readily arranged.
Furthermore the present invention provides a magneto-optical disk apparatus applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a drive signal generation circuit generating a first drive signal including a first timing at which a first alternating magnetic field is applied, and a second drive signal including a second timing at which a second alternating magnetic field is applied; a first magnetic head operating based on the first drive signal to apply the first alternating magnetic field to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium; a second magnetic head operating based on the second drive signal to apply the second alternating magnetic field to the magnetic domain at the other edge existing in the direction of the track; a first optical head directing a first laser beam to the one edge; and a second optical head directing a second laser beam to the other edge; and a composite circuit compositing together a first magneto-optical signal detected at the first timing and a second magneto-optical signal detected at the second timing, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present magneto-optical disk apparatus, a drive signal generation circuit generates first and second drive signals and in response to the first drive signal a first alternating magnetic field is applied to any magnetic domain at one edge and in response to the second drive signal a second alternating magnetic field is applied to any magnetic domain at the other edge. Furthermore, first and second laser beams are directed to one and the other edges, respectively, independently. Then, attributed to any magnetic domain having opposite ends initially transferred and enlarged two magneto-optical signals are detected and the detected two magneto-optical signals are composited together.
Thus in the present invention two drive signals can be used to apply two alternating magnetic fields to any magnetic domain at opposite ends and attributed to any magnetic domain having opposite ends initially transferred and enlarged there can be detected two magneto-optical signals to obtain a reproduced signal depending on a domain length of each magnetic domain.
Preferably the magneto-optical disk apparatus further includes a delay time calibration circuit determining an optimal phase difference between a first detection signal obtained by reproducing through the first alternating magnetic field and the first laser beam a recorded signal corresponding to an alternation of a magnetic domain representing a unit bit of 1 and a magnetic domain representing a unit bit of 0 and a second detection signal obtained by reproducing the recorded signal through the second alternating magnetic field and the second laser beam, the optimal phase difference corresponding to a clock count corresponding to a distance between an optical axis of the first laser beam and an optical axis of the second laser beam. Furthermore, the composite circuit composites the first magneto-optical signal and the second magneto-optical signal together based on the optimal phase difference.
An adjustment is made to provide an optimal phase difference between a first detection signal obtained through a first alternating magnetic field and a first laser beam and a second detection signal obtained through a second alternating magnetic field and a second laser beam. Then, first and second magneto-optical signals are detected and the first and second magneto-optical signals have their phase difference set to be the optimal phase difference and the two magneto-optical signals are thus composited together.
Thus, in the present invention, attributed to any magnetic domain having opposite ends initially transferred and enlarged, there can be detected two magneto-optical signals which are in turn composited together to accurately obtain a reproduced signal depending on a domain length of each magnetic domain.
Furthermore, preferably when in the magneto-optical disk apparatus L represents a distance between the optical axis of the first laser beam and the optical axis of the second laser beam and d represents a length of a magnetic domain created in the magneto-optical recording medium and representing a unit bit, as seen in the direction of the track, L/d represents the clock count corresponding to the distance between the optical axis of the first laser beam and the optical axis of the second laser beam.
For a magnetic domain, first and second magneto-optical signals have therebetween an optimal phase difference determined as a clock count corresponding to a distance between the optical axes of two laser beams.
Thus in the present invention if two laser beams have their respective optical axes spaced by a unit domain length provided in a magneto-optical recording medium that is multiplied by an integer then two magneto-optical signals can be accurately composited together with an optimal phase difference.
Furthermore, the present invention provides a signal reproduction method applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a first step of applying a first alternating magnetic field and directing a first laser beam to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium, and applying a second alternating magnetic field and directing a second laser beam to the magnetic domain at the other edge existing in the direction of the track of the magneto-optical recording medium; a second step of detecting a first magneto-optical signal through the first alternating magnetic field and the first laser beam and a second magneto-optical signal through the second alternating magnetic field and the second laser beam; and a third step of compositing the first and second magneto-optical signals together, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present signal reproduction method, attributed to any magnetic domain created in a magneto-optical recording medium and having opposite ends initially transferred and enlarged two magneto-optical signals are detected which are in turn composited together to obtain a reproduced signal.
Thus in the present invention there can be obtained a reproduced signal depending on a domain length of each magnetic domain and hence accurately.
Furthermore the present invention provides a signal reproduction method applying a laser beam and a magnetic field to reproduce a signal from a magneto-optical recording medium having a magnetic domain created therein to record a signal therein, including: a first step of applying a first alternating magnetic field and directing a first laser beam to any magnetic domain at one edge existing in a direction of a track of the magneto-optical recording medium, and applying a second alternating magnetic field and directing a second laser beam to the magnetic domain at the other edge existing in the direction of the track of the magneto-optical recording medium; a second step of determining an optimal phase difference between a first detection signal obtained by reproducing through the first alternating magnetic field and the first laser beam a recorded signal corresponding to an alternation of a magnetic domain representing a unit bit of 1 and a magnetic domain representing a unit bit of 0 and a second detection signal obtained by reproducing the recorded signal through the second alternating magnetic field and the second laser beam, the optimal phase difference corresponding to a clock count corresponding to a distance between an optical axis of the first laser beam and an optical axis of the second laser beam; a third step of detecting a first magneto-optical signal through the first alternating magnetic field and the first laser beam and a second magneto-optical signal through the second alternating magnetic field and the second laser beam; and a fourth step of setting a phase difference between the first and second magneto-optical signals to be the optimal phase difference determined at the second step, and compositing the first and second magneto-optical signals together, wherein the first alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the one edge, and the second alternating magnetic field contains a magnetic field component having a predetermined angle to a plane of the direction of the track and increasing an in-plane component of a leaking magnetic field created at the other edge.
In the present signal reproduction method, a first detection signal obtained through a first alternating magnetic field and a first laser beam and a second detection signal obtained through a second alternating magnetic field and a second laser beam have therebetween a phase difference set to be an optimal phase difference. Then, first and second magneto-optical signals are detected and the detected two magneto-optical signals have their phase difference set to be the optimal phase difference and the two magneto-optical signals are thus composited together.
Thus in the present invention there can be obtained a reproduced signal corresponding to each domain length provided in a magneto-optical recording medium.
Preferably, when L represents a distance between the optical axis of the first laser beam and the optical axis of the second laser beam and d represents a length of a magnetic domain created in the magneto-optical recording medium and representing a unit bit, as seen in the direction of the track, L/d represents the clock count corresponding to the distance between the optical axis of the first laser beam and the optical axis of the second laser beam.
For a magnetic domain, first and second magneto-optical signals have therebetween an optimal phase difference determined as a clock count corresponding to a distance between the optical axes of two laser beams and the two magneto-optical signals are thus composited together.
Thus in the present invention if two laser beams have their respective optical axes spaced by a unit domain length provided in a magneto-optical recording medium that is multiplied by an integer then two magneto-optical signals can be composited together with an optimal phase difference. Thus a signal can be reproduced accurately.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.